Stress Relaxation of Thermo-Reversible Gels. Polyvinyl Alcohol–Congo Red–Water System

Stress relaxation curves were obtained for the gels of the polyvinyl alcohol-conga red-water system in the temperature range, 15∼60°C, by means of a chainomatic relaxometer. The molecular weight of polyvinyl alcohol was 8.5×104, and gels of 15.0 and 17.5% were used, where the concentration of congo red was adjusted to be 1/10 of that of polyvinyl alcohol. Master relaxation curves were obtained for each concentration over the range, 10−2∼109hr, and relaxation spectra were calculated by the second order approximation. The following results were obtained. 1) The logaT vs. T relation gives a single curve for two concentrations, and does not obey the equation of WLF form, Also it has characteristics similar to that of agar-agar gels. 2) The apparent activation energy is kept constant to be 42 kcal. below about 43°C, and above this temperature it sharply increases with temperature. 3) The reduction on concentration to a single composite relaxation curve seems to be possible in rough approximation.